1. The Field of the Invention
This invention relates to photography. More precisely, the invention disclosed herein relates to an improved method for preparing intermediates for the formation of metal complexed dyes useful in the formation of photographic image patterns.
2. Description of the Prior Art
Compounds conforming to the following formula are known to the art. ##SPC2##
Wherein each R can be hydrogen, an alkyl substituent, preferably a lower alkyl substituent having from 1-6 carbon atoms or an alkoxy substituent preferably a lower alkoxy substituent having from 1-6 carbon atoms, R.sup.1 is hydrogen or an alkyl or alkanol group preferably having from 1-8 carbon atoms. R.sup.2 is an alkylene radical having from 1-6 carbon atoms and X represents the atoms to complete a cyclopentyl or cyclohexyl ring. Details relating to compounds of the above formula can be found in commonly assigned U.S. Pat. No. 3,551,406 and U.S. Pat. No. 3,563,739 both issued to Elbert M. Idelson on Dec. 29, 1970 and Feb. 16, 1961 respectively. A representative compound conforming to Formula 1 is as follows: ##SPC3##
Various procedures for preparing chrome complexes of Formula 1 are disclosed in U.S. Pat. No. 3,551,406. For example, one of these disclosed syntheses employed prior to the present invention in an effort to obtain the desired chrome complexes on a production scale includes the steps of
1. REACTING THE NON-COMPLEXED AZO DYE WITH A CHROMIC SALT TO FORM A CHROME COMPLEX THEREOF;
2. REACTING THIS COMPLEX WITH A PROTECTED DERIVATIVE OF THE DESIRED LIGAND-DEVELOPER, E.G., A DERIVATIVE WHEREIN THE HYDROXYL GROUPS OF THE DIHYDROXYPHENYL SILVER HALIDE DEVELOPING SUBSTITUENT ARE REPLACED WITH CATHYLOXY (--OCOOC.sub.2 H.sub.5) groups to form the corresponding 1:1 chrome complex; and
3. HYDROLYZING TO REMOVE THE PROTECTIVE GROUPS AND TO FORM THE DESIRED DIHYDROXYPHENYL SUBSTITUENT, THEREBY FORMING THE DESIRED CHROMIUM COMPLEX.
This sequence of reactions may be illustrated as follows: ##SPC4##
This method of synthesis has certain disadvantages from the standpoint of large scale production, chief of which are the need for the "deblocking" step of removing the protective groups, the inherent problem of having one of the protected derivatives remaining, and the fact that the alkali employed in the deblocking step causes some removal of the ligand from the complex as well as formation of oxidation product and alkali product contaminants.
Accordingly, a particularly preferred system for preparing the desired chrome complexes in large scale production would be one of the other alternative syntheses disclosed in the patent employing the free dihydroxyphenyl ligand-developer, thereby eliminating the third step and the problems inherent in the use of the protected derivative. For this reason, prior to the present invention efforts were directed to this latter synthetic group.
Early in the synthesis work for preparing these chrome complexes it was discovered that a base, e.g., an amine such as triethylamine, was needed as an acid acceptor in order to make the ligand react with the chrome complex formed in step one. While the exact reaction mechanism with this amine is not entirely understood, it is known that the amine reacts with or in some way "picks up" the acid, e.g., the hydrochloric acid formed by the chroming reaction illustrated above in step one. However, while the chrome compound formed in step one may be reacted with the free ligand-developer in the presence of such a base to form the desired 1:1 chrome complex including the ligand-developer moiety, it has been found that certain reaction by-products are produced which may be regarded as impurities and which are not easily separable from the desired chrome complex. These impurities are apparently reaction products between the amine and the azo dye, perhaps due to the amine "competing" with the ligand-developer in the second reaction step. Thus, if the amine reacts with the azo dye faster than does the ligand, the wrong product will be obtained. It has been found that the use of more hindered amines such as tri-n-butyl amine or ethyldiisopropylamine could be advantageously employed to avoid formation of impurities in an analagous reaction described in commonly assigned copending application Ser. No. 164,103 filed July 19, 1971 by Henry Bader and Edwin J. Jahngen, Jr. wherein a dihydroxyphenyl ligand was reacted with a yellow dye chromophore. However, despite the use of more hindered amines, in the present reaction between the ligand developer and the chrome complexed compound of step 1, enough of this impurity is obtained to adversally affect the contemplated use of this chrome complex in color photography. To appreciate the nature and seriousness of this problem, some basic knowledge of the function of the chrome complex in preparing color images is necessary.
These complexes are intended primarily for use as one of the three dyes in a film unit intended for preparing multicolor images in accordance with the color diffuson transfer procedures described and claimed in U.S. Pat. No. 2,983,606.
In such procedures a photosensitive element intended for accurate color reproductions of the original subject matter will be of the so-called "tripack" configuration including three sets of selectively sensitized silver halide layers, each having a dye developer (a) dye which is also a silver halide developing agent) of specified color associated therewith:
1. a silver halide layer sensitive to red light having a cyan dye developer associated therewith;
2. a silver halide layer sensitive to green light having a magenta dye developer associated therewith; and
3. a silver halide layer sensitive to blue light having a yellow dye developer associated therewith.
When a film unit of this configuration is exposed to visible light to provide a developable image and is then contacted with an aqueous alkaline solution which permeates through the respective layers and dissolves the aforementioned dye developers, each dye developer develops the exposed and, therefore, developable silver halide grains of the associated silver halide layer and is in turn oxidized to provide an oxidation product of the dye developer which is less soluble and less diffusible in the aqueous alkaline solution than is the unoxidized (unreacted) dye developer. There is thus provided an imagewise distribution of unoxidized dye developer in terms of unexposed areas of the associated silver halide layer, which imagewise distribution is free to diffuse or be transferred by imbibition to a superposed dyeable stratum to impart thereto a color transfer image. When none of the three silver halide layers are exposed in a given area, none of the dye developers associated therewith are oxidized and hence all three are available to transfer to provide a black image corresponding to these three areas. In other words, these three dyes together provide a black color. Conversely, when all three silver halide layers are exposed in a given area, all three dye developers are in turn oxidized as a function of development of these areas and no dye should be transferred, so that the transfer image should appear to be white in these areas. If only one of these silver halide layers is exposed and thus rendered developable, the other two dyes should be free to transfer to provide a color aproximating the color of the light exposing that one layer. For example, assume that the magenta dye developer is one of the chrome complexes to which this invention is directed and is therefore associated with the green-sensitive silver halide layer. When green subject matter is photographed, the green light reflected from this subject matter selectively exposes the green-sensitive silver halide layer and does not render the other two silver halide layers developable. When the thus exposed element is thereafter developed, only the magenta dye developer which develops the associated green-sensitive (exposed) silver halide layer is oxidized and thereby immobilized and the yellow dye developer and cyan dye developer associated with the other two silver halide layers is transferred to the dyeable stratum. Since cyan plus yellow dye provide a green color, the original green subject matter is reproduced. In like manner the various other colors of the visible stratum are reproduced so that if the sensitometric design of the film unit as well as its efficiency is optimum, accurate or faithful color image reproductions of the original subject matter are provided. On the other hand, if dye is transferred which should not be transferred or, conversely, if insufficient dye intended to be transferred is not transferred, the quality of the resulting dye transfer image will suffer accordingly.
With the foregoing background information in mind, the problem of having the aforementioned impurities caused by the amine reacting with the azo dye present along with the desired chrome complex will best be appreciated. These impurities may be of substantially the same color, i.e., possess substantially the same spectral absorption characteristics of the desired chrome complexes. While the presence of such an impurity of substantially the same color would not necessarily be detrimental in non-photographic applications of dye, e.g., in the dying of a fabric or the like, the presence of such an impurity seriously effects the quality of a photographic image employing a chrome complex including such impurities in the aforementioned photographic system for preparing dye images. The impurity will have no developing substituent attached as does the desired chrome complex. Thus, there is no imagewise control of the impurity and instead of being oxidized and thereby immobilized in order to have selective imagewise transfer of this particular color, the impurity will be free to transfer and will therefore diffuse to the dyeable stratum both in exposed and in non-exposed areas of the associated silver halide layer. Accordingly, in areas where no magenta dye is intended, this magenta (or whatever other color it may be) impurity will appear. Areas of the transfer image which are intended to appear white will, therefore, appear faintly colored or altered by this impurity. In like manner, due to the presence of this impurity, the colored or other image areas intended to be magenta-free will also be stained and the color of the image thus adversely effected by the presence of this impurity.
It is to this problem that the present invention is directed.